Roll forging machines have upper and lower rolls forming a set. The rolls include dies which rotate at the same speed but in opposite directions. The dies on the rolls form side-by-side rolling passes. Heated stock is moved sequentially through the passes and the rotating dies move the stock between the rolls forging the metal in a desired shape and length. Roll forging machines vary substantially in size and stock is fed through the various roll passes by tongs or grippers which may be manually or automatically manipulated. Examples of roll forging machines are those manufactured by Ajax Manufacturing Company of Cleveland, Ohio and as seen in U.S. Pat. No. 3,033,063.
The manipulation of stock through the various roll passes must be done with some precision and swiftly to achieve both forging accuracy and efficient production rates. For example, each pass requires a start and gauging or pick-up position which may vary from pass to pass. Also, since the stock is growing in length from pass to pass and must normally be rotated 90.degree. about its axis between each pass, the manual manipulation of the stock requires great skill and strength, particularly for heavy stock.
Efforts have been made to mechanize the feed or manipulation of the stock in roll forging machines and reference may be had to the mechanical system shown in Schiller U.S. Pat. No. 3,338,081. While mechanical drive feed mechanisms may be acceptable with certain simplified stock and rolling operations, they are unable to provide the sophistication necessary for special shapes or more complex roll forging operations. For example, the stroke lengths in the "X" direction (aligned with the passes) cannot readily be varied, nor can the gauge points be adjusted for each pass or from pass to pass, nor can the start or gauge points readily be adjusted on the fly, or while the machine is in operation.
If an automatic feed for a roll forging machine can provide for setting up and adjusting differential pick-up or gauging positions from pass to pass, much more complex parts can be roll forged with precision and at lower cost. For example, tapered parts considerably longer than the peripheral die length can be rolled on smaller diameter or half round dies. Smaller forging rolls and dies are considerably less costly. Also, accurate gauge point correction greatly reduces roll die development and adjustment time which reduces cost. With a mechanical system this is essentially impossible because the stock has to be moving at essentially the speed of the dies at the gauging position.
Also, after the stock has been engaged it is desirable that the feed or stock gripper move into a freewheeling mode so that the stock is moved by the dies until released by the forging dies. However, during such mode it is desirable to exert a small compression or tension bias on the stock depending on the type of stock. For example for short parts a slight compression or drag is desirable while for long slender parts, a slight tension may be desirable to prevent buckling. Moreover the desired bias may change as the dies wear. This cannot be accomplished with a mechanical feed which is itself of course subject to wear.
In some roll forging operations it is preferred that the initial or heaviest pass be in the middle of the roll with subsequent passes on each side of the initial pass. This for example provides for greater flexibility of die design and extended life of roll shaft bearings. This cannot be accomplished with an automatic feed if that feed is limited to sequential traversing in the "Y" direction or transverse the passes. Thus non-sequential traversing which can readily be changed is highly desirable.
It is of course important that movement of the stock or throughput of the machine be entirely automatic so that the stock is fed to and discharged from the machine without operator assistance. It is also important that the stock be at a correct forging temperature before moving through the machine lest damage to the machine or a scrap preform or finished roll part result. A preform is a roll forged part which is subject to subsequent forging on other types of equipment.
It is also important that the machine including the feed occupy as little floor space as possible, that the feed can be retrofitted readily on existing forging machines, and that the machine be readily serviced.